Table Top Not Flat

[Chuck Keysor]

Hello Shopbot friends:

When recently cutting a V-carving, I noticed line widths that should have been even, were not. As carving proceeded in the increasing X axis direction, the lines got narrower when they should have stayed the same width.

Being in a rush, I put a shim under the low end of my plaque to raise it up about .030" and that made it so I could finish my V-carving. After that carving was done, I decided to re-flatten my table top using my 2 1/2" Amana planing bit.

The next time I did a V-carving, I noticed the same problem, and thought maybe my planing bit had slipped in the collet. So I flattened my table top again, and made sure the collet was tight. Well, the problem still exists, my table is still not flat.

I did some measuring of the area on my table top that I use the most, from (2,5) to (36, 30). Those readings are in the attachment. (I measured the gap using a set of "feeler" gauges. I didn't want to try and measure right on my table edges, lest I drop my feeler gauges onto the floor.)

The summary of what I found:
Moving along the line from (2,5) to (36,5), the table drops .010"
Moving along the line from (2,15) to (31,15), the table drops .036"
Moving along the line from (2,30) to (36,30), the table drops .049"

Any suggestions as to how I can fix this? I have no idea how this could happen,,,,,, as even if the rails were messed up, the gantry should have held a fixed distance from the table top.

Thank you, I hope this makes sense....... Chuck

[Chuck Keysor]

PS: In making my measurements, I installed a 60 degree V-bit into my spindle. I zeroed the bit at the edge of my table (1,30) and used that Z height (of the spindle) for all subsequent measurements.

I moved the bit to (2,30) then used feeler gauges to measure the gap between the tip of the V-bit and the table top. Then moved to (3,30), measured the gap, moved to (4,30) and so on............

[cowboy1296]

I get my wood planks from a furniture maker who finishes them by running them through a 50 inch wide drum sander. Even still my planks are not perfectly flat and i always plane them flat before starting a project or at least they are in tune with my table top. Now this does not address your table but just relating my experience. Before i started the process of planning i noticed a plaque that came out like you described.

[bobmoore]

Chuck it sounds like maybe your spoilboard or plenum is springing up in the corner where you zero it. The amana bit is pretty good quality so I wouldn't suspect the shank is slipping in the collet unless your collet is worn out.

[Chuck Keysor]

Thanks guys for the replies. As notes, my collet is pretty new, maybe 2 years old now, but to my embarrassment, it has low miles.... And the fact that I really tightened it down before flattening the second time pretty much eliminates the only thing that I can think would create such a problem.

The material I have been carving is manufactured material that is also very flat Vinyl Composite Tile. And I used to carve this material with good success (uniform line widths when doing small V-carved letters) on tiles that are 12" x 12".

My spoil board/plenum assembly is all glued together and is very solidly bolted to the steel frame members. Hmmmmmmmmmmm................ Chuck

[fredtoo]

Environmental conditions - temp or humidity variations?

Vertical play in "Z"?

Hmmmmmmmm.......